An electromagnetic pole and coil assembly includes a magnetizing coil composed of a plurality of turns of copper wire. The several turns of the coil are electrically insulated one from the other as by a coating or wrapping on the wire or by means of insulating spacers placed between the several turns. In some instances combinations of two or more of the foregoing may be used for more effective turn-to-turn insulation. The magnetizing coil surrounds a magnetizable ferrous metal pole piece (e.g., steel) and is electrically insulated therefrom by a material or materials known as ground insulation positioned in the annular interspace between the coil and the pole. Typical ground insulations used heretofore have included mica sheets, resin impregnated glass wrappings, silicon rubber, and a variety of thermoplastic and thermosetting resins (e.g., epoxy) injected into the pole-coil interspace.
The power output of a dynamo-electric machine can be increased by increasing the current flow through its field and/or armature (and correspondingly the interpoles) coils. Increasing the current flow, however, also increases the temperature of the coils. The power output rating of a machine is often limited only by the ability of the pole-and-coil's insulation system to withstand high temperature excursions resulting from transient high current loadings.
The current carrying capacity of the coils could be increased without increasing temperature by providing more copper therein, and accordingly less resistance. If the pole and coil's insulation system were to remain the same, increasing the copper content of the coils would require a costly increase in the physical size (i.e., volume/shape) of the machine's external housing and related parts. However, room for additional coil copper might be found within the confines of a standard-size machine housing if a more efficient insulation system could be devised. A more efficient insulation system would provide high temperature stability and good thermal conductivity yet consume less space than heretofore required without sacrificing dielectric protection. The converse is also true. In this regard, a more efficient insulation system could permit the coil to run hotter and thereby permit reduction in the amount of coil copper without reducing output ratings.
Ideally, the insulation system of a pole and coil assembly for use in severe service environments will perform several important functions simultaneously. In this regard, the insulation: will rapidly dissipate heat generated within the coil to the ambient and the pole; will aid in anchoring the coil substantially immovably with respect to the pole; and will not only provide adequate pole-to-coil ground insulation but also have sufficient thermal stability to withstand high temperature thermal excursions without breaking down.
It is an object of the present invention to provide a pole and coil assembly having a highly efficient insulation system which is characterized not only by good dielectric properties, good thermal conductivity and high temperature thermal stability but also serves to so unite the coil and pole together as to enhance the ruggedness thereof. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.